nginx proxy-cache-lock (via) Crucially important feature hidden away in the nginx documentation: proxy_cache_lock enables request coalescing, or dog-pile protection: it means that if a hundred simultaneous requests all suffer the same cache miss, only one request is made to the backend and the answer is then sent back to all hundred requests at once. I’ve leaned heavily on this feature in Varnish for years—useful to know that nginx has the same capability.